The Asian water monitor has a natural affinity towards water, inhabiting the surroundings of lakes, rivers, ponds, swamps and various riparian habitats, including sewers, city parks, and urban waterways. It is an excellent swimmer and hunts fish, frogs, invertebrates, water birds, and other types of aquatic and amphibious prey. Due to its apparently large, stable population, it is currently listed as Least Concern on to the IUCN Red List.
Etymology
The generic name Varanus is derived from the Arabicwaral (ورل), which translates as "monitor". The specific name is the Latin word for "saviour", denoting a possible religious connotation.[2] The water monitor is occasionally confused with the crocodile monitor (V. salvadorii) because of their similar scientific names.[3]
Some common names for the species are Malayan water monitor, common water monitor, two-banded monitor, rice lizard, ring lizard, plain lizard, no-mark lizard and water monitor etc.
The family Varanidae contains nearly 80 species of monitor lizards, all of which belong to the genus Varanus.[5] There is a significant amount of taxonomic uncertainty within this species complex. Morphological analyses have begun to unravel this taxonomic uncertainty but molecular studies are needed to test and confirm the validity of certain groupings within this genus. Research initiatives such as these are very important to assess changes in conservation assessments.[1]
The black water monitor from Thailand's Satun Province and Thai-Malaysian border area was formerly the subspecies V. s. komaini, but now is regarded as a junior synonym and melanistic population of V. s. macromaculatus.[7]
Description
Head closeup showing split tongueWalking on pavement
The Asian water monitor is dark brown or blackish with yellow spots on the underside that fade gradually with age. It has blackish bands with yellow edges extending back from each eye. Its body is muscular, with long, powerful, laterally compressed tails. Its scales are keeled; the ones on top of the head are larger than those on the back. Its neck is long and the snout elongated. It has powerful jaws, serrated teeth and sharp claws.[9]
Adults rarely exceed 1.5–2m (4ft 11in– 6ft 7in) in length, but the largest specimen on record from Sri Lanka measured 3.21m (10.5ft). A common mature weight is 19.5kg (43lb).[9] However, 80 males killed for the leather trade in Sumatra averaged only 3.42kg (7.5lb) and 56.6cm (22.3in) snout-to-vent and 142cm (56in) in total length; 42 females averaged 3.52kg (7.8lb) and 59cm (23in) snout–vent length and 149.6cm (58.9in) in total length.[9] Males are larger than females and attain breeding maturity at a length of 40cm (16in) and a weight of 1kg (2.2lb); and females at a length of 50cm (20in).[9]
A series of adults weighed 7.6kg (17lb).[10] Mature individuals in northern Sumatra were estimated to have a mean estimated body mass of 20kg (44lb).[11] A sample of 55 Asian water monitors weighed 2–32kg (4.4–70.5lb).[12] The maximum weight of captive individuals is over 50kg (110lb).[13]
In captivity, Asian water monitors' life expectancy has been determined to be anywhere between 11 and 25 years depending on conditions, in the wild it is considerably shorter.[14][15]
The Asian water monitor is widely distributed from India, Bangladesh, Sri Lanka, Myanmar and Thailand, Cambodia, Laos, Vietnam, the Chinese Guangxi and Hainan provinces, Malaysia, Singapore to the Sunda islandsSumatra, Java, Bali, Borneo and Sulawesi. It inhabits primarily lowland freshwater and brackish wetlands. It has been recorded up to an elevation of 1,800m (5,900ft).[1]
The Asian water monitor is semiaquatic and opportunistic; it inhabits a variety of natural habitats though predominantly resides in primary forests and mangrove swamps. It has been noted that it is not deterred from living in areas near human civilization. In fact, it has been known to adapt and thrive in agricultural areas as well as cities with canal systems, such as in Sri Lanka, where they are not hunted or persecuted. Habitats that are considered to be most important are mangrove vegetation, swamps, wetlands, and elevations below 1,000m (3,300ft). It does not thrive in habitats with extensive loss of natural vegetation and aquatic resources.[1]
Behaviour and ecology
Water monitors robbing eggs from a nest. Illustration by Pierre Jacques Smit from Richard Lydekker's The Royal Natural History, 1893–1896Asian water monitor resting on a rubber tireHatchlingJuvenile
Water monitors defend themselves using their tails, claws, and jaws. They are excellent swimmers, using the raised fin on their tails to steer through water. When encountering smaller prey items, the water monitor will subdue it in its jaws and proceed to violently thrash its neck, destroying the prey's organs and spine which leaves it dead or incapacitated. The lizard will then swallow it whole.
In dominantly aquatic habitats, their semiaquatic behavior is considered to provide a measure of safety from predators. This along with their versatile diet is said to contribute to their plasticity, or ecological adaptability.[1] When hunted by predators such as the king cobra (Ophiophagus hannah) they will climb trees using their powerful legs and claws. If this evasion is not enough to escape danger, they have also been known to jump from trees into streams for safety, a tactic similar to that of the green iguana (Iguana iguana).[14]
Like the Komodo dragon, the water monitor will often eat carrion,[2][16] or rotten flesh. By eating this decaying flesh, the lizard provides benefits to the ecosystem by removing infectious elements, cleaning the environment.[17] They have a keen sense of smell and can smell a carcass from far away.
The first description of the water monitor and its behaviour in English literature was made in 1681 by Robert Knox, who observed it during his long confinement in the Kingdom of Kandy: "There is a Creature here called Kobberaguion, resembling an Alligator. The biggest may be five or six feet long, speckled black and white. He lives most upon the Land, but will take the water and dive under it: hath a long blue forked tongue like a sting, which he puts forth and hisseth and gapeth, but doth not bite nor sting, tho the appearance of him would scare those that knew not what he was. He is not afraid of people, but will lie gaping and hissing at them in the way, and will scarce stir out of it. He will come and eat Carrion with the Dogs and Jackals, and will not be scared away by them, but if they come near to bark or snap at him, with his tail, which is long like a whip, he will so slash them, that they will run away and howl."[18]
Water monitors are prone to attacking humans when threatened, and should be handled with caution. The bite of a water monitor can inflict a severe injury.
Reproduction
The Asian water monitor breeds between April and October. The females will lay their eggs about a month after mating in rotting logs or stumps. A clutch can vary from 10 to 40 eggs with an incubation period of 6 to 7 months. When hatched, hatchlings are fully developed and independent. Once males and females reach a length of about 1 meter and 50 centimeters, respectively, they will become reproductively mature and able to breed.[citation needed]
Diet
Asian water monitor at Kandy Lake (Bogambara lake), Sri Lanka. Possibly obese or gravid, or both.
They are carnivores, and consume a wide range of prey. They are known to eat fish, frogs, rodents, birds, crabs, and snakes.[2] They have also been known to eat turtles, as well as young crocodiles and crocodile eggs.[19] Water monitors have been observed eating catfish in a fashion similar to a mammalian carnivore, tearing off chunks of meat with their sharp teeth while holding it with their front legs and then separating different parts of the fish for sequential consumption.[20]
As carnivores and scavengers,[21] the diet of the Asian water monitor in an urban area in central Thailand includes fish, crabs, Malayan snail-eating turtles (Malayemys macrocephala), Chinese edible frogs (Hoplobatrachus rugulosus), birds, small rodents, domestic cats (Felis catus) and dogs (Canis familiaris), chickens (Gallus gallus domesticus), food scraps and carcass.[22] They are known to feed on dead human bodies. While on the one hand their presence can be helpful in locating a missing person in forensic investigations, on the other hand they can inflict further injuries to the corpse, complicating ascertainment of the cause of death.[23] The stomachs of 20 adult Asian water monitors caught on Redang Island contained mostly human food waste, followed by turtle eggs and hatchlings, crabs and lizard eggs.[24] The monitor does not thrive in these areas, but manage to still live in them. Studies are being conducted in order to understand how these creatures are able to do so in and around human civilization.[25]
Venom
The possibility of venom in the genus Varanus is widely debated. Previously, venom was thought to be unique to Serpentes (snakes) and Heloderma (venomous lizards). The aftereffects of a Varanus bite were thought to be due to oral bacteria alone, but recent studies have shown venom glands are likely to be present in the mouths of several, if not all, of the species. The venom may be used as a defensive mechanism to fend off predators, to help digest food, to sustain oral hygiene, and possibly to help in capturing and killing prey.[26][27]
Predation
Adult water monitors have few natural predators, and are only known to be preyed on by saltwater crocodiles (Crocodylus porosus).[28]
Threats
Young V. s. macromaculatus. Video clip
Monitor lizards are traded globally and are the most common type of lizard to be exported from Southeast Asia, with 8.1 million exported between 1998 and 2007 for the international leather market.[29] Today the most harvesting for water monitors in Southeast Asia occur in Indonesia and Peninsular Malaysia.[30] The Asian water monitor is one of the most exploited varanids; its skin is used for fashion accessories such as shoes, belts and handbags which are shipped globally, with as many as 1.5 million skins traded annually[1] and between 50,000 and 120,000 skins harvested from the wild in Peninsular Malaysia.[30] Other uses include a perceived remedy for skin ailments and eczema,[31] novelty food in Indonesia,[32] and a perceived aphrodisiac,[33] and as pets.[34] In India, several tribal communities hunt these monitor lizards for their meat, fat and skin and the eggs are also harvested. They are often considered as pests and their populations are also threatened by habitat loss and habitat fragmentation.[35]
Conservation
Roadway crossing sign, Thailand
In Nepal, it is a protected species under the Wild Animals Protection Act of 2002. In Hong Kong, it is a protected species under Wild Animals Protection Ordinance Cap 170. In Malaysia, this species is one of the most common wild animals, with numbers comparable to the population of macaques there. Although many fall victim to humans via roadkill and animal cruelty, they still thrive in most states of Malaysia, especially in the shrubs of the east coast states such as Pahang and Terengganu as the regulations in Malaysian states differ based on wildlife management authorities.[36] In Thailand, all monitor lizards are protected species.[34] It is still common in large urban areas in Thailand and is frequently seen in Bangkok's canals and parks. Because of this, it is currently listed as Least Concern in the IUCN Red List. These classifications have been made on the basis that this species maintains a geographically wide distribution, can be found in a variety of habitats, adapts to habitats disturbed by humans, and is abundant in portions of its range despite large levels of harvesting.[1]
Loss of habitat and hunting has exterminated water monitors from most of mainland India. In other areas they survive despite being hunted, due in part to the fact that larger ones, including large females that breed large numbers of eggs, have tough skins that are not desirable.[37]
In Sri Lanka, it is protected by local people who value its predation of "crabs that would otherwise undermine the banks of rice fields".[37] It is also protected as it eats venomous snakes.[38]
The Komodo dragon, also known as the Komodo monitor, is a member of the monitor lizard family Varanidae that is endemic to the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang. It is the largest extant species of lizard, growing to a maximum length of 3 m (9.8 ft), and weighing up to 70 kg (150 lb).
Monitor lizards are lizards in the genus Varanus, the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are recognized.
Megalania is an extinct species of giant monitor lizard, part of the megafaunal assemblage that inhabited Australia during the Pleistocene. It is the largest terrestrial lizard known to have existed, reaching an estimated length of 3.5 to 7 metres, and weighing between 97–1,940 kg (214–4,277 lb), but the fragmentary nature of known remains make estimates highly uncertain.
The Great Nicobar Biosphere Reserve encompasses a large part of the island of Great Nicobar, the largest of the Nicobar Islands in the Indian Union Territory of Andaman and Nicobar Islands. The Nicobars lie in the Bay of Bengal, eastern Indian Ocean, 190 km (120 mi) to the north of the Indonesian island of Sumatra. The reserve has a total core area of approximately 885 km2, surrounded by a 12 km-wide "forest buffer zone". In year 2013 it was included in the list of Man and Biosphere program of UNESCO to promote sustainable development based on local community effort and sound science.
The Nile monitor is a large member of the monitor family (Varanidae) found throughout most of Sub-Saharan Africa, particularly in drier regions, and along the Nile River and its tributaries in East Africa. Additionally, there are modern, invasive populations in North America. The population found in West African forests and savannahs is sometimes recognized as a separate species, the West African Nile monitor. While it is dwarfed by its larger relatives, such as the Komodo dragon, the Asian water monitor or the crocodile monitor, it is still one of the largest lizards in the world, reaching Australia’s perentie in size. Other common names include the African small-grain lizard, as well as iguana and various forms derived from it, such as guana, water leguaan or river leguaan.
The Bengal monitor, also called the Indian monitor, is a species of monitor lizard distributed widely in the Indian subcontinent, as well as parts of Southeast Asia and West Asia.
The perentie is a species of monitor lizard. It is one of the largest living lizards on earth, after the Komodo dragon, Asian water monitor, and the Crocodile monitor. Found west of the Great Dividing Range in the arid areas of Australia, it is rarely seen, because of its shyness and the remoteness of much of its range from human habitation. The species is considered to be a least-concern species according to the International Union for Conservation of Nature.
The desert monitor is a species of monitor lizard of the order Squamata found living throughout North Africa and Central and South Asia. The desert monitor is carnivorous, feeding on a wide range of vertebrates and invertebrates.
The lace monitor, also known as the tree goanna, is a member of the monitor lizard family native to eastern Australia. A large lizard, it can reach 2 metres (6.6 ft) in total length and 14 kilograms (31 lb) in weight. The lace monitor is considered to be a least-concern species according to the International Union for Conservation of Nature.
The spiny-tailed monitor, also known as the Australian spiny-tailed monitor, the ridge-tailed monitor the Ackie dwarf monitor, and colloquially simply ackie monitor, is an Australian species of lizard belonging to the genus of monitor lizards (Varanus).
The rock monitor is a species of monitor lizard in the family Varanidae. The species is endemic to Sub-Saharan Africa, where, on average it is the largest lizard found on the continent. It is called leguaan or likkewaan in some areas.
The yellow-headed water monitor, also commonly known as Cuming's water monitor, the Mindanao water monitor, and the Philippine water monitor, is a large species of monitor lizard in the family Varanidae. The species is endemic to the Philippines. It thrives in mangrove, forest and water margins in tropical refuges, where it feeds on birds, fishes, mammals, and carrion.
The turquoise monitor is a species of monitor lizards found in Indonesia. Specifically, it is found on Halmahera Island and in the Maluku Islands.
The black rough-necked monitor is a species of monitor lizard found in Southeast Asian countries of Thailand, Burma, and Malaysia. It is also found in Indonesia on Sumatra and islands of the Riau Archipelago It is sometimes known simply as the roughneck monitor. In Thailand is called h̄èā cĥāng.
Dumeril's monitor is a species of lizard in the family Varanidae. The species is endemic to Southeast Asia.
The marbled water monitor, also known commonly as the Philippine water monitor, is a large species of monitor lizard in the family Varanidae. The species is endemic to the Philippines.
Varanus zugorum, also known commonly as the silver monitor or Zugs' monitor, is a species of monitor lizard in the family Varanidae. The species is endemic to the island of Halmahera in the Moluccas, in Indonesia.
Varanus spinulosus, the Solomon Island spiny monitor, Isabel monitor, or spiny-neck monitor, is a species of monitor lizard. It is endemic to the Solomon Islands archipelago and is also known from Santa Isabel Island, San Jorge Island and Bourgainville Island.
Hapturosaurus, sometimes known as the tree monitors, is a subgenus of lizards, consisting of slender-bodied arboreal monitor lizards mostly found in the tropical rainforests of Indonesia and Papua New Guinea.
↑ Laurenti, J. N. (1768). "XC. Stellio salvator". Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena[Medical Treatise, Exhibiting an Emended Synopsis of Reptiles, with Experiments Concerning Venoms and Antidotes for Austrian Reptiles]. Viennae: Joan. Thomae. p.58.
1 2 3 Koch, A. (2007). "Morphological studies on the systematics of South East Asian Water Monitors (Varanus salvator Complex): Nominotypic populations and taxonomic overview". Mertensiella. 16 (109): e80.
1 2 3 4 Shine, R.; Harlow, P. S. & Keogh, J. S. (1996). "Commercial harvesting of giant lizards: The biology of water monitors Varanus salvator in southern Sumatra". Biological Conservation. 77 (2–3): 125–134. Bibcode:1996BCons..77..125S. doi:10.1016/0006-3207(96)00008-0.
↑ Dryden, G. L.; Green, B.; Wikramanayake, E. D. & Dryden, K. G. (1992). "Energy and water turnover in two tropical varanid lizards, Varanus bengalensis and V. salvator". Copeia. 1992 (1): 102–107. doi:10.2307/1446540. JSTOR1446540.
↑ Shine, R.; Harlow, P. S. (1998). "Ecological traits of commercially harvested water monitors, Varanus salvator, in northern Sumatra". Wildlife Research. 25 (4): 437−447. doi:10.1071/WR97118.
↑ Salakij, C.; Salakij, J.; Prihirunkit, K.; Narkkong, N.-A.; Sanyathitiseree, P.; Kranjanapitukkul, K. (2014). "Quantitative and qualitative morphologic, cytochemical, and ultrastructural characteristics of blood cells in captive Asian water monitors". Veterinary Clinical Pathology. 43 (4): 538–546. doi:10.1111/vcp.12183. PMID25123583.
↑ "Varanus salvator". World Association of Zoos and Aquariums. Archived from the original on 30 April 2015. Retrieved 22 August 2012.
↑ Rahman, K. M. M.; Rakhimov, I. I.; Khan, M. M. H. (2017). "Activity budgets and dietary investigations of Varanus salvator (Reptilia: Varanidae) in Karamjal ecotourism spot of Bangladesh Sundarbans mangrove forest". Basic and Applied Herpetology. 31: 45–56. doi:10.11160/bah.79.
↑ Knox, R. (1681). An Historical Relation of the Island of Ceylon in the East Indies: Together With, an Account of the Detaining in Captivity the Author, and Divers, Other Englishmen Now Living There, and of the Author's Miraculous Escape. London: Richard Chiswell.
↑ Whitaker, R. (1981). "Bangladesh – Monitors and turtles". Hamadryad. 6 (3): 7–9.
↑ Khadiejah, S., Abu-Hashim, A.K., Musa, F.H., Abdul-Patah, P., Abdul-Rahman, M.T., Ismail, H.I., Wahab, A., and Razak, N.A. (2020). Management and Trade in Asian Water Monitors (Varnanus salvator) in Peninsular Malaysia. Department of Wildlife and National Parks Peninsular Malaysia (PERHILITAN). 87 pages.
↑ Wirz, P. (1954). Exorcism and the Art of Healing in Ceylon. Leiden: Brill. p.238.
Further reading
Das, I. (1988). "New evidence of the occurrence of water monitor (Varanus salvator) in Meghalaya". Journal of the Bombay Natural History Society. 86: 253–255.
Deraniyagala, P. E. P. (1944). "Four New Races of the Kabaragoya Lizard Varanus salvator". Spolia Zeylanica. 24: 59–62.
Pandav, B. (1993). "A preliminary survey of the water monitor (Varanus salvator) in Bhitarkanika Wildlife Sanctuary, Orissa". Hamadryad. 18: 49–51.
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